3,437 research outputs found
Money in Gas-Like Markets: Gibbs and Pareto Laws
We consider the ideal-gas models of trading markets, where each agent is
identified with a gas molecule and each trading as an elastic or
money-conserving (two-body) collision. Unlike in the ideal gas, we introduce
saving propensity of agents, such that each agent saves a fraction
of its money and trades with the rest. We show the steady-state money
or wealth distribution in a market is Gibbs-like for , has got a
non-vanishing most-probable value for and Pareto-like when
is widely distributed among the agents. We compare these results with
observations on wealth distributions of various countries.Comment: 4 pages, 2 eps figures, in Conference Procedings of International
Conference on "Unconventional Applications of Statistical Physics", Kolkata,
India, March 2003; paper published in Physica Scripta T106 (2003) 3
Enhanced grain surface effect on magnetic properties of nanometric La0.7Ca0.3MnO3 manganite : Evidence of surface spin freezing of manganite nanoparticles
We have investigated the effect of nanometric grain size on magnetic
properties of single phase, nanocrystalline, granular La0.7Ca0.3MnO3 (LCMO)
sample. We have considered core-shell structure of our LCMO nanoparticles,
which can explain its magnetic properties. From the temperature dependence of
field cooled (FC) and zero-field cooled (ZFC) dc magnetization (DCM), the
magnetic properties could be distinguished into two regimes: a relatively high
temperature regime T > 40 K where the broad maximum of ZFC curve (at T = Tmax)
is associated with the blocking of core particle moments, whereas the sharp
maximum (at T = TS) is related to the freezing of surface (shell) spins. The
unusual shape of M (H) loop at T = 1.5 K, temperature dependent feature of
coercive field and remanent magnetization give a strong support of surface spin
freezing that are occurring at lower temperature regime (T < 40 K) in this LCMO
nanoparticles. Additionally, waiting time (tw) dependence of ZFC relaxation
measurements at T = 50 K show weak dependence of relaxation rate [S(t)] on tw
and dM/dln(t) following a logarithmic variation on time. Both of these features
strongly support the high temperature regime to be associated with the blocking
of core moments. At T = 20 K, ZFC relaxation measurements indicates the
existence of two different types of relaxation processes in the sample with
S(t) attaining a maximum at the elapsed time very close to the wait time tw =
1000 sec, which is an unequivocal sign of glassy behavior. This age-dependent
effect convincingly establish the surface spin freezing of our LCMO
nanoparticles associated with a background of superparamagnetic (SPM) phase of
core moments.Comment: 41 pages, 10 figure
Effects of different doses of x-rays on meiotic chromosomes of malePhysopelta schlanbuschi (Largidae: Heteroptera)
Male largid bugs,Physopelta schlanbuschi, having 2n=17 chromosomes (12 autosomes +2m+X1X2Y), were irradiated with x-ray doees of 300 r, 400 r and 500 r which yielded various types of chromosome aberrations in different stages of meiosis of which the common forms were breaks, fragment of unknown origin, constriction, gap etc. Among the 3 sex chromosomes, the two conspicuously large markers, X1 and Y, sometimes formed chiasmalike configuration in prophase I and metaphase I, while a number of anaphase I plates had a chromatid bridge, very likely formed by the X1 and the Y. The qualitative and quantitative assessments of chromosome aberrations in spermatogonial metaphase, prophase I, metaphase I, anaphase I and metaphase II were made at 13 intervals for the doses of 300 r and 400 r and 14 intervals for 500 r between 5 min and 1 week or more. The data showed over-all dose-dependent aberration effects and the sex chromosomes appeared relatively more vulnerable than the autosomes to different doses of x-rays. The testes of untreated males taken as controls had practically no aberration
Nonuniversal exponents in sandpiles with stochastic particle number transfer
We study fixed density sandpiles in which the number of particles transferred
to a neighbor on relaxing an active site is determined stochastically by a
parameter . Using an argument, the critical density at which an
active-absorbing transition occurs is found exactly. We study the critical
behavior numerically and find that the exponents associated with both static
and time-dependent quantities vary continuously with .Comment: Some parts rewritten, results unchanged. To appear in Europhys. Let
Order Parameter and Scaling Fields in Self-Organized Criticality
We present a unified dynamical mean-field theory for stochastic
self-organized critical models. We use a single site approximation and we
include the details of different models by using effective parameters and
constraints. We identify the order parameter and the relevant scaling fields in
order to describe the critical behavior in terms of usual concepts of non
equilibrium lattice models with steady-states. We point out the inconsistencies
of previous mean-field approaches, which lead to different predictions.
Numerical simulations confirm the validity of our results beyond mean-field
theory.Comment: 4 RevTex pages and 2 postscript figure
A generalized family of anisotropic compact object in general relativity
We present model for anisotropic compact star under the general theory of
relativity of Einstein. In the study a 4-dimensional spacetime has been
considered which is embedded into the 5-dimensional flat metric so that the
spherically symmetric metric has class 1 when the condition
is satisfied (
and being the metric potentials along with a constant ). A set of
solutions for the field equations are found depending on the index involved
in the physical parameters. The interior solutions have been matched smoothly
at the boundary of the spherical distribution to the exterior Schwarzschild
solution which necessarily provides values of the unknown constants. We have
chosen the values of as and =10 to 20000 for which interesting and
physically viable results can be found out. The numerical values of the
parameters and arbitrary constants for different compact stars are assumed in
the graphical plots and tables as follows: (i) LMC X-4 : ,
for and , for , (ii) SMC
X-1: , for , and , for . The investigations on the physical features of the model include
several astrophysical issues, like (i) regularity behavior of stars at the
centre, (ii) well behaved condition for velocity of sound, (iii) energy
conditions, (iv) stabilty of the system via the following three techniques -
adiabatic index, Herrera cracking concept and TOV equation, (v) total mass,
effective mass and compactification factor and (vi) surface redshift. Specific
numerical values of the compact star candidates LMC X-4 and SMC X-1 are
calculated for central and surface densities as well as central pressure to
compare the model value with actual observational data.Comment: 20 pages, 9 figures, 2 Table
Chaos in Sandpile Models
We have investigated the "weak chaos" exponent to see if it can be considered
as a classification parameter of different sandpile models. Simulation results
show that "weak chaos" exponent may be one of the characteristic exponents of
the attractor of \textit{deterministic} models. We have shown that the
(abelian) BTW sandpile model and the (non abelian) Zhang model posses different
"weak chaos" exponents, so they may belong to different universality classes.
We have also shown that \textit{stochasticity} destroys "weak chaos" exponents'
effectiveness so it slows down the divergence of nearby configurations. Finally
we show that getting off the critical point destroys this behavior of
deterministic models.Comment: 5 pages, 6 figure
Clustering properties of a generalised critical Euclidean network
Many real-world networks exhibit scale-free feature, have a small diameter
and a high clustering tendency. We have studied the properties of a growing
network, which has all these features, in which an incoming node is connected
to its th predecessor of degree with a link of length using a
probability proportional to . For , the
network is scale free at with the degree distribution and as in the Barab\'asi-Albert model (). We find a phase boundary in the plane along which
the network is scale-free. Interestingly, we find scale-free behaviour even for
for where the existence of a new universality class
is indicated from the behaviour of the degree distribution and the clustering
coefficients. The network has a small diameter in the entire scale-free region.
The clustering coefficients emulate the behaviour of most real networks for
increasing negative values of on the phase boundary.Comment: 4 pages REVTEX, 4 figure
Initiation sites for discontinuous precipitation in some Cu-base alloys
A systematic effort has been made to investigate the suitability of various interfaces, natural as well as artificial, to initiate discontinuous precipitation. The interfaces studied in the present investigation include sample surface (external), and grain and interphase boundaries. It has been demonstrated that in addition to grain boundaries, non-conventional initiation sites like coherent faces of a twin or eutectic/eutectoid boundaries under favourable conditions may also nucleate discontinuous precipitation. In general, the ability of an interface to undergo thermally activated migration appears to be the most important criterion for the initiation of discontinuous precipitation
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